Ab initio molecular-dynamics study of highly nonideal structural and thermodynamic properties of liquid Ni-Al alloys

Atomic and electronic structure, and diffusion coefficients in liquid Ni-Al alloys, have been calculated by ab initio molecular-dynamics simulations. The chemically short-range ordered structure of liquid Ni20Al80 measured by neutron scattering is well reproduced in these simulations. We calculate a significant electronic contribution (ΔSel=-0.4 kB/atom) to the formation entropy of NiAl at 1900 K, originating from a simultaneous narrowing and shifting of the Ni d band to higher binding energies accompanying alloying with Al. This value of ΔSel, combined with an estimate for the configurational entropy based on calculated radial distribution functions and a nonadditive hard-sphere model, accounts for the large negative excess entropy of mixing measured in liquid Ni-Al alloys.